1. Field of the Invention
The present invention relates generally to devices for and methods of detecting leaks in tanks for storing gasoline, oil and other liquids.
2. Description of the Prior Art
Heretofore, a number of procedures and devices have been used to detect leaks in underground liquid storage reservoirs. Mooney, U.S. Pat. 4,186,591 discloses a prior invention of the present inventor in which an underground liquid storage reservoir is filled with liquid until the level of the liquid rises into one or more hollow tube members extending upwardly above the top portion of the tank and communicating the interior of the tank with the ground surface; any change in the level of the liquid in the tube members over a period of time is measured; and any change in the temperature of the liquid in the reservoir over the same period of time is also measured. The present invention is an improvement over the device and method disclosed in U.S. Pat. No. 4,186,591 .
The inventor is also aware of the following patents that relate, in general, to the present invention; Hansel, U.S. Pat. Nos. 4,281,534 and Hansel, 4,300,388. These two Hansel patents relate to a sensor for and a method of measuring leakage in a tank by measuring any change in mass displacement over a period of time. The preferred sensor design is such as to compensate for changes due to evaporation of the liquid and changes occurring in density and the level of the liquid due to temperature variations. In general, the sensor comprises a cup portion for being suspended within the tank from a balance arm or other mass displacement detector. Compensation for evaporation results because any evaporation that occurs will occur from both the surface of the liquid in the tank and from the surface of liquid in the cup. The buoyancy of the liquid on the sensor is a function of the sensor diameter, but since the inside diameter of the cup is essentially the same as the outside diameter of the sensor, the evaporative loss of liquid from the cup will compensate for the buoyancy change due to evaporation of the liquid in the tank. Thus, when the liquid in the tank evaporates, its buoyant force is reduced and the sensor becomes heavier, but the evaporation of the liquid in the cup reduces the weight of the sensor by substantially the same amount and no change in the weight of the sensor occurs. Thus, these two Hansen patents relate to an automatic compensation method and does not involve measuring change in the elevation of liquid due to evaporation.
The prior art, taken as a whole, does not disclose or suggest the present invention.